Concept: International trade documents are formal papers needed to complete a cross-border transaction.
Explanation: An invoice is one of the principal documents prepared by the exporter and sent to the importer.
It details the nature of the goods, the quality, the quantity, the agreed price, and terms of payment.
It serves as proof of the contract and helps customs authorities assess duties.
Among the options given, the invoice is the only standard international trade document used in export and import operations.
A debit note and a credit note are internal or settlement documents, not the main cross-border shipping document.
A price ring is an arrangement among sellers, not a trade document.
Therefore, the correct option is C. Invoice.
Answer: C. Invoice